"We do not base these requirements on any knowledge that any individual USAG staff or board members had a role in fostering or obscuring Nassar's actions," Blackmun wrote. "Our position comes from a clear sense that USAG culture needs fundamental rebuilding."

Blackmun acknowledged the series of resignations and policy changes that USAG has experienced in recent months but he said it was not enough.

"USAG must build on them with a categorically fresh start at the board level," he wrote.

Along with the resignations, Blackmun outlined a series of additional steps required by the Olympic Committee, including:

•USAG has 12 months to replace the interim directors.

•USAG "must cooperate with an independent investigation" looking into whether anyone knew or should have known of abuse allegations against Nassar and did not report them.

•The board "must substantively discuss" progress and plans for continued implementation of the findings from a former prosecutor's lengthy report that highlighted an array of shortcomings by USA Gymnastics in combating abuse.

"Please understand that the circumstances that led to this crisis demand our attention and intervention," he wrote. "These steps are intended to help USAG create a culture that protects and supports its athletes in the way I know we all want to do."

In a statement Thursday night, USAG said it "completely embraces the requirements outlined" in Blackmun's letter and "appreciates the opportunity to work with the USOC to accomplish change for the betterment of our organization, our athletes and our clubs."

USA Gymnastics also said it understands "that the requirements imposed by the letter will help us enhance our ability to build a culture of empowerment throughout the organization, with an increased focus on athlete safety and well-being. Our commitment is uncompromising, and we hope everything we do makes this very clear."